Icephobic concrete is a slippery step closer

Ice is the enemy of infrastructure – roads, railway tracks, and footpaths can all be rendered useless in the depths of winter. Various anti-icing coatings are in common use in the automotive, maritime and aviation industries, but in almost all cases, these coatings are applied to relatively smooth, hard surfaces (e.g. metals, glass, and ceramics). With hierarchical porosity and high roughness, concrete offers a much tougher challenge to coatings developers. Ice forms and adheres very differently to concrete than to metals, making it difficult to remove once formed. And repeated freezing events can cause concrete to crack, costing cities millions of dollars in repairs a year.

This has prompted a growing number of research teams to explore icephobic surfaces – durable coatings that could be applied directly to concrete-like materials to reduce ice adhesion. Writing in the December issue of Materials Letters [DOI: 10.1016/j.matlet.2018.09.008], team of polymer scientists from Donghua University in Shanghai report on their latest development – a two-step spray process that works on standard concrete tiles.

They first analysed the hydrophobic and icephobic properties of pristine concrete samples. The contact angle was found to vary over time – dropping from 57.5° to 18° in 14 minutes. This is the result of water penetrating into the concrete structure through open pores on the surface. The coated concrete tiles were prepared by spraying a diluted fluorine resin directly onto the surface – this acted as the adhesive layer. The team’s superhydrophobic coating consisted of fluorosilane-functionalized silica (F-SiO2) nanoparticles suspended in isopropanol. Three layers of this – measuring several hundred nanometers – were sprayed on top. SEM imaging showed the structural changes this made to the concrete, and the coated samples also displayed a constant contact angle of 165.5°, making them superhydrophobic.
Cold water dropped onto both samples also behaved differently on each; quickly spreading on the pristine concrete, and forming spherical droplets on the coated sample. This observation was reflected in the measured ice adhesion strength – it was found to be ten times lower on coated concrete than on uncoated concrete. Both samples went through thirty icing-de-icing cycles, too, with the coated concrete outperforming the coated in all cases. However, beyond this, the superhydrophobic coatings began to suffer structural damage, reducing its performance. In practical terms, this means that the coating would need to be regularly reapplied.